The first cards to reference a teammate came in Unglued, relegated to silver-border, as the rules didn't yet support the concept. Imperial Mask, from Future Sight, was the only one to exist in black border for 9 years, until the release of the surge mechanic in Oath of the Gatewatch. A Two-Headed Giant-focused supplementary set Battlebond was released on June 8, 2018, featuring 14 cards referencing either teams or teammates.
- In a multiplayer game between teams, a player’s teammates are the other players on their team. See rule 102.3.
- 102.3. In a multiplayer game between teams, a player’s teammates are the other players on their team, and the player’s opponents are all players not on their team.